120/240 SERVICE

[blues]

I have an existing service rated for 120/240V, 3phase, 4wire (Three single phase xfmrs on a pole). Owner wants to install new kitchen equipment will be rated for 208V along with new lighting. My question can 208V rated eq. run on 240V. Also is there an issue with 120v lighting on what I assume is high-leg delta service?

Thanks

 

[kwired]

Can be issues with equipment designed only for 208 volts. Motors will likely be fine the majority of the time unless they are designed to operate real close to full load rating and especially for long periods of time. Resistance type loads will run higher than design temperature and very likely will shorten the life of that equipment. Electronics all depends on design of the equipment. These days you see some that stuff that has a range of voltage that is acceptable. Most common anymore being lighting drivers/ballasts that will run on anything between 120 and 277 nominal.

You can not run any load designed for 120 volts only directly from the high leg without transformation equipment being involved.

 

[powerpete69]

I'm never comfortable with incorrect voltages. "should work" and "shortens life of motor" etc.
Suggest a 240V to 208V transformer to a 208/120 panelboard. Solves all issues.

 

[kwired]

I'm never comfortable with incorrect voltages. "should work" and "shortens life of motor" etc.
Suggest a 240V to 208V transformer. Solves all issues.

But you often can get away with running a 240 volt rated load on 208, especially resistance loads. For heating appliances it just takes a little longer to get same results, unless the equipment was marginally designed in the first place.

Motors have many things to consider, driven load vs rated load combined with cycle times. A motor that is typically used for short duty cycles, may never give you any troubles as it never gets heated up enough or long enough to cause much damage.

 

[powerpete69]

"But you can often get away with". Add that to the list.
I hear what you are saying.
However, the 208V loads may work on the 240V service.
They will for sure work on the 208V panelboard.

I guess you can tell the customer "it may work", "you can often get away with" and "it may shorten life". If he is all in, then you are certainly good to go. Make sure to get in writing that any problems that may occur are on the customer's dime.

Or install correct transformer and panelboard and done deal. Up to customer I suppose.

Understand this too, I come from a professional engineering consulting firm. Everything is either done 100% correct or not done at all.

 

[kwired]

"But you can often get away with". Add that to the list.
I hear what you are saying.
However, the 208V loads may work on the 240V service.
They will for sure work on the 208V panelboard.

I guess you can tell the customer "it may work", "you can often get away with" and "it may shorten life". If he is all in, then you are certainly good to go. Make sure to get in writing that any problems that may occur are on the customer's dime.

Or install correct transformer and panelboard and done deal. Up to customer I suppose.

Understand this too, I come from a professional engineering consulting firm. Everything is either done 100% correct or not done at all.

It comes down to if ordering new equipment, order units that are same or convertible to what you have on site. Warranties often are no good if not connected to rated voltage.

If buying used equipment part of reason for doing so is cost, inform owner of the risks and let them decide. Again there is more potential issues with running 208 rated equipment on 240 than there usually is running 240 rated equipment on 208. Every piece of equipment will have it's own set of conditions.

For OP an oven may see early failure of heating elements, if oven would have say a PID type controller it may not matter much, would only be an issue at times when it is calling for 100% output, which is probably only on cold starts. A disposer motor that only runs 30 seconds at a time maximum, may never notice any difference in performance or how long it will last.

 

[RD35]

The difference can really add up on resistive loads. I have project right now where a customer acquired used water heaters rated 208V 3phase 18KW each. They are listed as being reconnectable to single phase. However I am having to explain to the owner that the power draw for each water heater when reconnected will increase from 50amps (3-phase 208V) to 100amps (1-phase 240V). The combination of increased voltage and phase change doubles the amperage!

 

[kwired]

The difference can really add up on resistive loads. I have project right now where a customer acquired used water heaters rated 208V 3phase 18KW each. They are listed as being reconnectable to single phase. However I am having to explain to the owner that the power draw for each water heater when reconnected will increase from 50amps (3-phase 208V) to 100amps (1-phase 240V). The combination of increased voltage and phase change doubles the amperage!

And you will increase output to nearly 24 kW instead of 18.

Presuming there is three elements connected in delta configuration for three phase, you could get about 16 kW by just connecting two elements to the supply. Would draw about 66.6 amps.

If wye connected when in three phase wouldn't be able to do the single phase thing without using a neutral, but would be able to get exactly same output rating as three phase if you did use the neutral.

 

[topgone]

Your wild-leg point to your neutral will have a voltage of 208V. See here:

 

[augie47]

If Code matters
110.4 Voltages. Throughout this Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

 

[texie]

I have an existing service rated for 120/240V, 3phase, 4wire (Three single phase xfmrs on a pole). Owner wants to install new kitchen equipment will be rated for 208V along with new lighting. My question can 208V rated eq. run on 240V. Also is there an issue with 120v lighting on what I assume is high-leg delta service?

Thanks

I would not just assume that you have a 120/240 3 phase 4 wire service, particularly if there are 3 pots on the pole. In most areas that provide 3 phase high leg service it will be 2 pots open delta. 3 pots in most areas would likely indicate a 208Y service.
And as others said, in many cases you can operate equipment designed for 240 on a 208 system but not vice versa. With resistance heating equipment in particular, this could lead to serious problems.

 

[kwired]

I would not just assume that you have a 120/240 3 phase 4 wire service, particularly if there are 3 pots on the pole. In most areas that provide 3 phase high leg service it will be 2 pots open delta. 3 pots in most areas would likely indicate a 208Y service.
And as others said, in many cases you can operate equipment designed for 240 on a 208 system but not vice versa. With resistance heating equipment in particular, this could lead to serious problems.

Quite a bit of full delta with high leg around here. Retail, restaurants, offices... more likely to be wye, especially if newer building or newer remodeled.

Farms, small industrial, etc. with motor loads being majority of load, 240 delta is preferred. Little less amps for same load, can easily run single phase 240 volt equipment with no issues or at reduced power levels.

In more recent years farming operations have changed though, everything is bigger than it used to be. Big grain storage operation 30 years ago might have been three phase, very few were 480 volt three phase. Maybe only 50 - 100 HP of loads. Past few years most of those I have done were 480 three phase though, with sites that have 100-200 HP worth of motors or more.